A Guide To Dry Skin Disorders In The Lower Extremity

M. Joel Morse, DPM

   Ceramides are the natural moisturizing factors and are the major lipid constituents of the intercellular spaces of the stratum corneum. These lipids theoretically provide the barrier property of the epidermis.2 The link between skin disorders and changes in barrier lipid composition, especially in ceramides, is difficult to prove because of the many variables involved. However, most skin disorders that have a diminished barrier function present a decrease in total ceramide content with some differences in the ceramide pattern. Patients with skin diseases such as atopic dermatitis, psoriasis, contact dermatitis and some genetic disorders have diminished skin barrier function.6

   We continuously lose water from the skin’s surface by evaporation. Under normal conditions, the rate of loss is slow and the water is adequately replaced. Characteristic signs and symptoms of dry skin occur when the water loss exceeds the water replacement, and the stratum corneum’s water content falls below 10 percent.7

   Any factor that damages the stratum corneum can interfere with its barrier function and lead to dry skin. By and large, the feet are not subject to the typical factors that affect skin elsewhere including long, hot showers and cold, dry air, detergents and solvents. The feet are more subject to chafing and rubbing due to walking as well as the interplay between socks and shoes.

What You Should Know About Skin Structure And Ethnicity

A recent study has demonstrated that skin properties at the level of the stratum corneum vary considerably among ethnic groups.8 East Asian and Caucasian skin are characterized by low maturation and a relatively weak skin barrier. African-American skin is characterized by low ceramide levels and high protein cohesion in the uppermost layers of the stratum corneum.

   There is more transepidermal water loss in African-American skin than in Caucasian skin, predisposing patients to more xerosis. Ceramides are the major lipid constituent of lamellar sheets present in the intercellular spaces of the stratum corneum. These lamellar sheets provide the barrier property of the epidermis.2

   Ceramide levels in African-American skin are the lowest while Caucasians, Hispanics and Asians have the highest levels.9 So one can infer that black skin is more prone to xerosis and the pathology can be due to xerosis.

   African-American communities use the term “ashy” to describe dry skin. The skin is dry, cracked and powdery, and one can see the skin flakes more easily on dark skin. In our society, the ashy color is considered unacceptable and many African-Americans use oils or petrolatum to address this.10

   We generally regard moisturized skin as healthy and healthy looking. There may be corresponding changes in the optical properties when skin is moisturized.11 In healthy skin, there is less light scattering at the skin surface and more light penetration into the deeper skin layers when the skin is moisturized. As a result, the skin appears darker, more pinkish and more translucent.

   One popular moisturizer is shea butter. Shea butter is a yellow “fat” or “oil” extracted from the nut of the African shea tree. Complications of the use of occlusive emollients such as Vaseline and shea butter used on the dorsal foot and lower leg can result in “oil folliculitis” if the leg is hairy.

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